1. Field of the Invention
The present invention relates generally to automatic document feeders in media processing devices, and, more particularly, to media stack positioning mechanisms in input trays of automatic document feeders.
2. Description of the Related Art
Media handling devices such as laser or ink jet printers, scanners, copiers, fax machines, ATM machines and the like utilize many different types of pick mechanisms to deliver individual sheets of media to a delivery or indexing system of the device. It is known to load the media as a stack into an input tray before the individual pieces of media are fed to the system. A single piece of media is removed from the stack when processing occurs. In all such devices, the media must be fed reliably, one sheet at a time, each time a processing job occurs.
Both vertical and horizontal pick mechanism and media feed designs are known. Vertical mechanisms rely on both the user positioning of the stack in the input tray and gravity to bring the media stack to proper location in the input tray. Horizontal mechanism designs rely more exclusively on user positioning for proper orientation and placement of the media stack in the input tray. Some horizontal pick mechanisms have removable trays so that the user can visually recognize the proper position for the stack, and place the stack of media accordingly. Other horizontal designs do not employ removable trays, and the media stack is inserted into a fixed input tray area.
Proper and consistent positioning of the media stack in the input tray is essential to subsequent performance of the pick mechanism. Even after the stack of media has been positioned properly, it is important for all pieces of media to remain properly positioned, even as individual pieces are removed. If the stack of media is improperly positioned in the input tray, either initially or as individual pieces are removed, media-feeding failure can result. Improper feeding can cause media jams, skew of the media being delivered, or double and multiple picks of media from the input tray.
In both vertical and horizontal automatic document feeders it is known to use “block” mechanisms to aid in proper positioning of the media stack in the input tray. A block mechanism typically creates resistance to the insertion of the media stack, thereby providing positive feed back to the device user that the media is installed in a specific position. In vertical input trays, in which gravity can be used for final positioning, the block mechanism can be somewhat subtle, relying on the stack to settle into its final position under the influence of gravity, even after the user has released the stack. However, in horizontal input trays the block mechanism needs to provide an immediate, clear indication that the final media stack position has been reached. The user must not be tempted to terminate insertion too early, leaving the stack position short of the intended position, and must clearly be aware if the stack has been inserted too far.
Especially for horizontally oriented input trays, an advantageously designed media block apparatus, therefore, should fulfill two basic objectives. The block apparatus should convey a positive message to the user that the media stack is properly positioned, by providing a consistent and firm stopping location for media inserted into the input tray. Further, the block apparatus should maintain that position for the media stack relatively constantly as each sheet is removed from the tray and feed into the processing apparatus.
What is needed in the art is a simple, reliable and robust blocking mechanism that ensures proper stack positioning in a horizontal media input tray of a media processing device.